Consumers are constantly concerned about brittle, chipped, nails and dry, flyaway hair. Particularly for nails, there are many products which claim to strengthen nails and promote the growth of strong, healthy nails. For example, it is well known that formaldehyde and derivatives thereof are effective in strengthening nail keratin because such compounds are said to cross-link the proteins found in nail keratin. However, formaldehyde in particular, is generally considered undesireable for use on nails because it is known to be a sensitizer, particularly if used in the concentrations which are necessary to achieve appreciable nail hardening.
U.S. Pat. No. 3,349,000 teaches a method for treating human nails and hair with dimethylol thiourea, which is said to improve strength and elasticity. The patentee teaches that if compositions containing dimethylol thiourea are applied to nails or hair, these substrates are more resistant to cracking, splitting, laminating, or similar problems. While these compositions may work well, dimethylol thiourea contains sulfur, thus may have an unpleasant odor which consumers find unattractive.
U.S. Pat. No. 4,323,553 also teaches compositions used to strengthen and revitalize brittle or damaged nails, which contain 2-benzylthio ethylamine, another sulfur containing compound. This compound also contains sulfur and may provide an odor which consumers find unattractive.
U.S. Pat. No. 4,547,363 teaches a two part composition for strengthening nails. The first composition contains dimethylol ethylene thiourea and the second composition contains a polymerizable catalyst which contains an acid such as hydrochloric acid. The two compositions are mixed and applied to nails. This system is inconvenient because it requires the mixture of two separate compositions prior to use, which makes it more difficult for the consumer to use.
U.S. Pat. No. 5,785,959 teaches nail strengthening compositions which contain a permeation/binding agent, a thio cross-linking agent, and a chelating agent.
There is a need for compositions which further strengthen solid keratinous surfaces and, particularly with respect to fingernails, provide improved hardness, strength, and elasticity to the nail surface.